By Alexandra Keeler

Sustained drug use profoundly impacts brain function and physical health, leading to irreversible damage and long-term health risks

On Jan. 3, the US’s top doctor made headlines for recommending that alcoholic drinks include health warnings about their cancer risks. Alcohol consumption is a leading preventable cause of cancer, U.S. Surgeon General Dr. Vivek Murthy’s advisory notes.

Murthy’s recommendation comes amidst mounting attention to the health risks of alcohol consumption. In 2023, the World Health Organization sparked controversy when it said “no level of alcohol consumption is safe for our health.”

But all substance use affects the body, sources say, with illegal substances damaging nearly every organ in the body. Yet, the health effects of illegal substances receive relatively little attention.

“If you’ve ever looked at a population of people with substance use disorder [and] compared them to the general population, they would be worse off in terms of their cardiovascular risk,” said Dr. Christopher Labos, a Montreal-based cardiologist and host of The Body of Evidence podcast.

Several confounders

Illicit drugs like fentanyl, heroin and cocaine affect the body in all sorts of ways. But isolating their direct effects can be difficult, experts say, due to the social factors that often accompany addiction.

“People who are suffering from substance use disorder probably have poor nutrition, probably don’t exercise as much,” said Labos.

“Anybody who’s suffering from these problems is going to have several confounders that are going to increase the risk of cardiovascular disease.”

But Labos says cocaine is known to be the most damaging to the heart.

“In terms of which [illegal] substances are directly damaging to the heart, we clearly have a number one winner, and that would be cocaine,” Labos said.

“Cocaine is the one that’s very deliberately going to lead to higher rates of atherosclerosis [thickened artery walls] by increasing your heart rate, increasing your blood pressure and actually having a direct effect on thrombosis, so clogging of the arteries,” he added.

Opioids such as fentanyl and heroin also influence heart activity, Labos says. They lengthen the QT interval — a measure of heart electrical activity — which increases the risk of abnormal heart rhythms and potentially life-threatening cardiac issues.

Brain injury is another significant risk associated with illicit drug use.

Mauricio Garcia-Barrera, a psychology professor at the University of Victoria, says opioids such as fentanyl and heroin cause respiratory depression, leading to oxygen deprivation in the brain that damages brain cells.

“Between one to two minutes [after overdose, before resuscitation], the brain damage can start initiating, and between five minutes of cells in the brain not receiving oxygen, then we have the death of brain cells,” said Garcia-Barrera.

By contrast, stimulants like cocaine accelerate brain aging by damaging neurotransmitters, causing grey matter loss that leads to cognitive decline and impaired decision-making.

Brain changes

Neuropsychologist Carolyn Lemsky is the clinical director of Community Head Injury Resource Services, a Toronto not-for-profit that runs a brain rehabilitation program.

Lemsky says many of her patients want to quit using substances. But habitual drug use alters brain structure and function, making it difficult to quit.

“In people who use opioids and who have a lot of these non-fatal overdoses, their brain changes in many ways,” said Lemsky.

The brain atrophies in critical areas like the hippocampus, the region responsible for memory, and the temporal lobes. Simultaneously, neural pathways linked to habitual behaviour “get a little fatter,” reinforcing addiction.

This rewiring “tilts the brain toward immediate gratification,” Lemsky said. Meanwhile, impairments in the hippocampus diminish the ability to recall the negative consequences of past actions, making recovery even more challenging.

But Lemsky says alcohol remains the most problematic substance for her clients, due to its widespread use.

And while it is a legal substance, alcohol also affects the brain, she says. It leads to cognitive issues like memory and executive functioning problems. Many of her clients develop alcohol-related dementia due to vitamin deficiencies caused by chronic alcohol use.

Cannabis, another legal substance, has also become “more and more problematic” for her clients over the past 15 years, Lemsky says.

“Cannabis also interferes with cognitive functioning,” she said.

According to Health Canada’s 2024 cannabis survey, 80 per cent of Canadians recognize cannabis can be habit-forming and detrimental to youth brain development. Only 71 per cent said they were aware it is linked to mental health issues such as psychosis.

‘Further research is needed’

In a statement to Canadian Affairs, Health Canada said the long-term health consequences of illegal drug use require further study.

“Further research is needed to better understand long-term impacts of opioid-related harms, including the relationship between brain injury and substance use, as well as predisposing factors and long-term effects,” said Marie-Pier Burelle, a media relations advisor for Health Canada.

Lemsky says it is problematic that the Canadian Drugs and Substances Strategy — the government’s framework for addressing substance use-related harms — does not address the known health effects of illegal drugs.

“If you look at the Canada drug strategy, it doesn’t mention brain or cognition once,” she said.

In 2022, NDP MP Alistair MacGregor introduced Bill C-277, a private member’s bill that aims to establish a national strategy on brain injuries. The bill was at the report stage when Parliament was prorogued in early January. Further work on the bill could resume in the next parliamentary session.

“They need a brain injury strategy,” says Lemsky, explaining that cognitive impairment is the leading reason people disengage from medical support services, such as getting treatment for addiction.

“The treatment has too high a cognitive load and isn’t adapted to their needs,” she said. “They can’t manage, and they leave.”

This article was produced through the Breaking Needles Fellowship Program, which provided a grant to Canadian Affairs, a digital media outlet, to fund journalism exploring addiction and crime in Canada. Articles produced through the Fellowship are co-published by Break The Needle and Canadian Affairs.